CVAC Gasoline
CVAC Cam can be designed to optimize gasoline engines for any need. As the lobe design does not need to follow the traditional egg-shaped ones used in standard and variable camshafts, new valves opening and closing diagrams can be used.
An example of gasoline intake cam is shown to explain CVAC variability capabilities. Taking into account that CVAC lobes can be freely defined, this is just one of its infinite possible designs with the only purpose to show its unique capabilities that cannot be matched with any available mechanical Variable Valve Timing (VVT) or Variable Valve Actuator (VVA).
In the design below, you can see an example of a CVAC intake cam. This is a 2D representation where different lobes are shown in a standard timing diagram.
Below you can see the same example of the CVAC cam in a 3D representation. The third axis representing the follower position is added. The follower is placed in desired lobe position using an electromagnetic positioner that is managed by the engine’s ECU.
This graph shows five differentiated sections (L0 to L1, L2 to L3, …) each designed to let the engine work in a specific mode:
Cylinder deactivation mode
The Cylinder deactivation section is from lobes L0 to L1. The lift is zero for the whole rotation of the crank. This defines a standard cylinder deactivation technique of closing both intake and exhaust valves. The 2D timing diagram is not shown, because it has a zero elevation for the crankshaft rotation, but the section is highlighted in the 3D figure below. CVAC is cylinder independent variable camshaft, so any piston can be deactivated in any given time.
Idle mode
The Idle section is between lobes L1 to L2 and it starts from a zero lift to a Late Intake Valve Opening (LIVO) to optimize idling and very low speeds and loads. This is shown in the figure below, where not only the L1 and L2 lobe can be used, but all the intermediate lobes (L1.1 and L1.2 as an example). Also this section is highlighted in the 3D figure below.
Transition mode
The Transition section is between lobes L2 to L3. To have a continuous 3D cam, this transition section is required to go from Idle mode to Atkinson mode and can be used when the low rpms and loads are required. This is shown in the 2D and 3D figures below:
Atkinson Cycle mode
The Atkinson section is between lobes L3 to L4. The Atkinson cycle in modern cars is achieved by the delaying the closing of the intake valve during the compression stroke, allowing fuel savings. This is shown in 2D and 3D figures below, where different late closing lobes are shown. Different late opening timings can be achieved (as L3.1) to tune the Atkinson cycle depending on the RPMs and loads of the engine.
Otto Cycle mode
The Atkinson cycle has a fuel economy advantage, but the Otto cycle has a better power to weight ratio and generates more power on the same engine. So at medium to large RPMs and loads the Otto cycle is used. The CVAC variability can be seen from starting a low RPM lobe opening almost at Top Dead Center (TDC) and closing shortly after Bottom Dead Center (BDC) in L4 lobe to a race lobe design; to have an early opening, late closing and with maximum lift in L5 one. Also intermediate lobes (as L4.1 and L4.2) will allow a perfect cam tuning for maximum torque and power in every RPMs of the engine. This is shown in 2D and 3D figures below.
Conclusion
A simple CVAC cam design is used as an example. But this simple cam has more variability possibilities than any other mechanical or pneumatic VVT or VVA in the market. It can be only achieved with camless solutions that are more complex, expensive and not available in the market (the only working solution is not known to be shared).